This invention relates to the use of esters of naphthenic acids and the higher or lower molecular weight analogs thereof, as dispersing agents for pigment additives such as carbon blacks, and encompasses pigment-dispersant compositions, processes of preparation thereof and coating and rubber compositions comprising a pigment thus dispersed. The dispersants of the present invention permit the preparation of various pigment dispersions which may be employed without adverse effects on the finished coatings or rubbers into which such dispersions may be incorporated.
One of the most difficult pigments to disperse and stabilize in a waterborne coating formulations or rubber compositions is carbon black, because of its enormous surface area and high oil absorption. Additionally, especially where a conductive carbon black pigment is to be utilized, it is important that the reduction of the electrostatic properties be minimized, and that the other physical characteristics of the final coating are not deleteriously affected by the particular pigment dispersant employed.
Naphthenic acid has been employed as a dispersing agent in printing inks where it has been shown to be a good dispersant for carbon black, and where it can improve fluidity and decrease clogging and gumming tendencies. (Lowar, Spec. Chem., April, 1989) Also, reference has been made in the art to the use of metal soaps of this acid as usable in the manufacture of pigments for paint, glazes, etc. (Kirk-Othmer's Encyclopedia of Chemical Technology, Volume 9, p. 246). However, the applicants know of no prior art reference directed to the use of esters of naphthenic acids as dispersants.
The products commonly employed in the prior art as carbon black dispersants in coatings are salts of an acrylic acid copolymer, acetylenic diol surfactants, or polyalcohol ethers which fit into various classes of wetting and dispersing agents, (Calbo, Handbook of Coatings Additives, Dekker pg. 516). Such additives could be called on to function as more than a dispersant and can also act in one or more of the following ways:
a) to prevent flocculation PA1 b) to prevent hard settling PA1 c) to improve jetness/color/gloss PA1 d) to control viscosity, and/or PA1 e) to improve wetting of the base resin. PA1 the inherent rheological stability of the dispersion, both alone and when added to a formulated paint; PA1 resistance to flocculation of the carbon black/dispersant mixture and in the final paint or coating; and PA1 ability to achieve low viscosity at high pigment loadings. PA1 high levels of dispersant may be required which tends to detrimentally affect the physical properties of formulated paints, such as adversely affecting the resultant humidity resistance, yellowing upon exposure to UV light, loss of cure in melamine cross-linked systems, and other undesirable effects; PA1 inability to prevent reflocculation of carbon black, resulting in the loss of electrical conductivity in dried paint films; and PA1 incompatibility of the dispersant with the particular resin system selected for use in the final paint formulation. PA1 excellent flocculation resistance of the dispersed black pigment; PA1 increased grinding efficiency; PA1 inherent rheological stability, that is low viscosity at high pigment loading; PA1 excellent dry film conductivity; and PA1 the humidity resistance of the formulated paint or film is not materially affected by use of claimed dispersants. PA1 where R.dbd.H or CH.sub.3, PA1 where n=1-6, and ##STR2## X=H or
Various considerations are important in determining the usefulness of any additive as a dispersing agent for use with a carbon black or with other pigments, depending upon the product into which such a dispersion is to be incorporated.
When used throughout this application the terms pigment(s) or pigment dispersion(s) are intended to encompass various materials which may be intended to impart either color and/or serve some other function, such as for example the use of carbon black in rubber where, in addition to adding color, such also acts as a reinforcing agent.
One of the most important considerations in determining whether a particular dispersant will be useful for use with a given pigment or pigments when such a pigment is to be used in a paint or coating composition is whether such a dispersant/pigment combination will or will not impart a conductive nature or characteristic to the dried paint film or coating into which it has been added.
The automotive industry is replacing and will continue to replace exterior metal body panels on vehicles with plastic and composite body panels. Some reasons for this change are weight reduction, flexibility of design, and lower tooling costs. The replacement of metal body panels by plastics and composites is not without difficulties.
One problem of note is the electrostatic spray painting of plastics. Electrostatic spray painting is the preferred manner of applying automotive topcoats. Spray painting normally gives the best appearance to the vehicle and the electrostatic technique assures the most economical use of the material. The problem arises because plastics do not paint well electrostatically unless a conductive primer is used.
Amongst the most important considerations for determining the utility of any dispersant to be used in conjunction with conductive carbon blacks are the following:
The various prior art references of which the applicants are aware which relate to dispersing agents for pigment additives, such as carbon blacks, suffer from a number of shortcomings.
The most significant shortcomings of the carbon black dispersants of the prior art, including those used for conductive carbon blacks, are:
The shortcomings of the prior art dispersing agents noted above may be overcome by employing certain naphthenic acid esters in accordance with the present invention.
It is therefore an object of the present invention to provide for novel carbon black and other pigment dispersions.
It is also an object of the present invention to provide a process for the preparation of pigment dispersions comprising the dispersants of the present invention for use in various coatings and rubbers.
It is a further object of the present invention to provide for improved coatings and rubbers incorporating the dispersants and dispersions taught herein.
It is another object of the present invention to provide an improved process for the production of various conductive coatings comprising the use of the dispersants and dispersions of the present invention.
Lastly, it is an object of the present invention to provide an improved process for the production of rubber compositions comprising the use of the dispersants and dispersions of the present invention.
These and other objects of the invention will be reflected in the course of the following for more detailed discussion.